In an ultrasonic flow meter, ultrasonic transducers emit ultrasonic signals into a flowing medium in order to measure the flow rate, or other parameters, of the flowing medium. Flowing liquids may contain gas bubbles, in particular air bubbles, which are continuously released from the liquid and into the pipe system. The released air bubbles reside in the pipe system as air pockets in cavities of the pipe system for a period of time until they are flushed away by the flowing liquid.
Ultrasonic flow meters installed in a pipe system may provide cavities in which released air can rest for a period of time. Air pockets in the pipe system need not be a problem, however for ultrasonic flow meters there is a risk that the air pockets interfere with the ultrasonic signal path and thereby interfere with the measurement and affect the accuracy. This is particularly a problem if the transducers reside at the highest point in the flow passage, since the space in front of the transducers may provide a cavity in which air can rest and adhere to the transducers.
In most compact flow meters, that is flow meters where the control electronics are mounted directly on the flow part, the control electronics as well as the display are positioned on the top side of the transducers. To avoid problems with gas bubbles that are caught in front of the transducers, the flow meter is rotated so that the transducers are moved away from the area of the highest point. However this results in that the display is also rotated away from a vertical view. Flow meters are installed in a variety of tube installation. In many situations, optimal visibility of the display would be achieved with a display pointing vertically upwards.
EP 1 967 828 A1 discloses a flow meter with a holding mechanism for a display which can be attached to a flow tube to ensure that the transducers are tilted away from the area of the highest point to avoid problems with air bubbles, while the display can be mounted in a horizontal plane to ensure a vertical viewpoint. While the problem with air bubbles is solved, the solution requires an elaborate holding mechanism.
DE 10 2007 011 547 A1 discloses, in FIG. 5, a flow meter where two transducers are inserted into the central area of the flowing fluid with opposing surfaces, since air bubbles by virtue of gravitation seek the top most part of the flowing fluid, such a flow meter construction would not have problems with air bubbles attaching to the transducers, irrespective of orientation of the flow tube. However, fabrication and mount of the transducer inserts is a difficult task.
WO 2007/020375 A1 discloses a flow meter where the transducers are mounted outside a bending flow tube, so that two transducer surfaces oppose each other in the central area of the flowing fluid. Such a flow meter construction would not have problems with air bubbles attaching to the transducers, irrespective of orientation of the flow tube. However, the meter construction requires a bend flow tube, opposing transducers and electrical connection of the transducers in the form of wires attached to the transducers and lead to the control electronics.